I know it is just a sock and I realize for a lot of people socks are an after thought, especially thin ones. But I have to say this sock rocks. I am the kind of guy that will wear a sock till its crusty and I got over a week in these bad boys before I had to wash them which you can't do at all with a cotton sock. Now, running in them may decrease the times you can use it before you have to wash them. As far as running in them I loved them as well. Wicks amazingly and keeps your feet feeling cool. For sizing I wear a 9.5 shoe which is where the large size begins but they just feel too big but the medium fits perfectly. Great sock!